Complex Systems Computational Laboratory

Cagliari, Italy

Complex Systems Computational Laboratory

Cagliari, Italy

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Zhu Z.,IMT Institute for Advanced Studies Lucca | Puliga M.,IMT Institute for Advanced Studies Lucca | Puliga M.,Complex Systems Computational Laboratory | Cerina F.,Complex Systems Computational Laboratory | And 5 more authors.
PLoS ONE | Year: 2015

The fragmentation of production across countries has become an important feature of the globalization in recent decades and is often conceptualized by the term "global value chains" (GVCs). When empirically investigating the GVCs, previous studies are mainly interested in knowing how global the GVCs are rather than how the GVCs look like. From a complex networks perspective, we use the World Input-Output Database (WIOD) to study the evolution of the global production system. We find that the industry-level GVCs are indeed not chain-like but are better characterized by the tree topology. Hence, we compute the global value trees (GVTs) for all the industries available in the WIOD. Moreover, we compute an industry importance measure based on the GVTs and compare it with other network centrality measures. Finally, we discuss some future applications of the GVTs. © 2015 Zhu et al.


Zhu Z.,IMT Institute for Advanced Studies Lucca | Cerina F.,University of Cagliari | Cerina F.,Complex Systems Computational Laboratory | Chessa A.,IMT Institute for Advanced Studies Lucca | And 7 more authors.
PLoS ONE | Year: 2014

Theory of complex networks proved successful in the description of a variety of complex systems ranging from biology to computer science and to economics and finance. Here we use network models to describe the evolution of a particular economic system, namely the International Trade Network (ITN). Previous studies often assume that globalization and regionalization in international trade are contradictory to each other. We re-examine the relationship between globalization and regionalization by viewing the international trade system as an interdependent complex network. We use the modularity optimization method to detect communities and community cores in the ITN during the years 1995-2011. We find rich dynamics over time both inter- and intra-communities. In particular, the Asia-Oceania community disappeared and reemerged over time along with a switch in leadership from Japan to China. We provide a multilevel description of the evolution of the network where the global dynamics (i.e., communities disappear or reemerge) and the regional dynamics (i.e., community core changes between community members) are related. Moreover, simulation results show that the global dynamics can be generated by a simple dynamic-edge-weight mechanism. © 2014 Zhu et al.


De Leo V.,Complex Systems Computational Laboratory | Santoboni G.,AECOM Technology Corporation | Cerina F.,Complex Systems Computational Laboratory | Cerina F.,University of Cagliari | And 8 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2013

This work analyzes methods for the identification and the stability under perturbation of a territorial community structure with specific reference to transportation networks. We considered networks of commuters for a city and an insular region. In both cases, we have studied the distribution of commuters' trips (i.e., home-to-work trips and vice versa). The identification and stability of the communities' cores are linked to the land-use distribution within the zone system, and therefore their proper definition may be useful to transport planners. © 2013 American Physical Society.


Borassi M.,IMT Institute for Advanced Studies | Chessa A.,IMT Institute for Advanced Studies | Chessa A.,Complex Systems Computational Laboratory | Caldarelli G.,IMT Institute for Advanced Studies | And 2 more authors.
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2015

In this work, we analyze the hyperbolicity of real-world networks, a geometric quantity that measures if a space is negatively curved. We provide two improvements in our understanding of this quantity: first of all, in our interpretation, a hyperbolic network is "aristocratic", since few elements "connect" the system, while a non-hyperbolic network has a more "democratic" structure with a larger number of crucial elements. The second contribution is the introduction of the average hyperbolicity of the neighbors of a given node. Through this definition, we outline an "influence area" for the vertices in the graph. We show that in real networks the influence area of the highest degree vertex is small in what we define "local" networks (i.e., social or peer-to-peer networks), and large in "global" networks (i.e., power grid, metabolic networks, or autonomous system networks). © 2015 American Physical Society. ©2015 American Physical Society.


Puliga M.,IMT Inc | Puliga M.,Complex Systems Computational Laboratory | Flori A.,IMT Inc | Pappalardo G.,IMT Inc | And 3 more authors.
PLoS ONE | Year: 2016

The role of Network Theory in the study of the financial crisis has been widely spotted in the latest years. It has been shown how the network topology and the dynamics running on top of it can trigger the outbreak of large systemic crisis. Following this methodological perspective we introduce here the Accounting Network, i.e. the network we can extract through vector similarities techniques from companies' financial statements. We build the Accounting Network on a large database of worldwide banks in the period 2001-2013, covering the onset of the global financial crisis of mid-2007. After a careful data cleaning, we apply a quality check in the construction of the network, introducing a parameter (the Quality Ratio) capable of trading off the size of the sample (coverage) and the representativeness of the financial statements (accuracy). We compute several basic network statistics and check, with the Louvain community detection algorithm, for emerging communities of banks. Remarkably enough sensible regional aggregations show up with the Japanese and the US clusters dominating the community structure, although the presence of a geographically mixed community points to a gradual convergence of banks into similar supranational practices. Finally, a Principal Component Analysis procedure reveals the main economic components that influence communities' heterogeneity. Even using the most basic vector similarity hypotheses on the composition of the financial statements, the signature of the financial crisis clearly arises across the years around 2008. We finally discuss how the Accounting Networks can be improved to reflect the best practices in the financial statement analysis. © 2016 Puliga et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.


de Montis A.,University of Sassari | Caschili S.,University College London | Chessa A.,Complex Systems Computational Laboratory | Chessa A.,University of Rome La Sapienza | Chessa A.,Institute for Advanced Studies Lucca
European Physical Journal: Special Topics | Year: 2013

A major issue for policy makers and planners is the definition of "ideal" regional partitions, i. e. the delimitation of sub-regional domains showing a sufficient level of homogeneity with respect to some specific territorial features. In this paper, we compare some intermediate body partitions of Sardinia, Italy, with patterns that emerge from the workers and students' commuting. We apply grouping methodologies based on the characterization of Sardinian commuting system as a complex weighted network. We adopt an algorithm based on the maximization of the weighted modularity of this network and detect productive basins composed by municipalities with degree of cohesiveness in terms of commuters' flows. The results of this study lead us to conclude that the recently instituded provinces in Sardinia have been designed -even unconsciously- as labour basins of municipalities with similar commuting behaviour. © 2013 EDP Sciences and Springer.


de Montis A.,University of Sassari | de Montis A.,Complex Systems Computational Laboratory | Caschili S.,University of Cagliari | Chessa A.,Complex Systems Computational Laboratory | Chessa A.,University of Cagliari
Journal of Geographical Systems | Year: 2011

The aim of this paper is to study the dynamics of the commuting system of two insular regions of Italy, Sardinia and Sicily, inspected as complex networks. The authors refer to a 20-year time period and take into account three census data sets about the work and study-driven inter-municipal origin-destination movements of residential inhabitants in 1981, 1991 and 2001. Since it is likely that the number of municipalities (in this case, the vertices of the system) does not display sharp variations, the authors direct the study to the variation of the properties emerging through both a topological and a weighted network representation of commuting in the time periods indicated. © 2010 Springer-Verlag.


Goncalves B.,Indiana University Bloomington | Perra N.,Indiana University Bloomington | Perra N.,Complex Systems Computational Laboratory | Vespignani A.,Indiana University Bloomington | Vespignani A.,Institute for Scientific Interchange
PLoS ONE | Year: 2011

Microblogging and mobile devices appear to augment human social capabilities, which raises the question whether they remove cognitive or biological constraints on human communication. In this paper we analyze a dataset of Twitter conversations collected across six months involving 1.7 million individuals and test the theoretical cognitive limit on the number of stable social relationships known as Dunbar's number. We find that the data are in agreement with Dunbar's result; users can entertain a maximum of 100-200 stable relationships. Thus, the 'economy of attention' is limited in the online world by cognitive and biological constraints as predicted by Dunbar's theory. We propose a simple model for users' behavior that includes finite priority queuing and time resources that reproduces the observed social behavior. © 2011 Gonçalves et al.


Cerina F.,University of Cagliari | Cerina F.,Complex Systems Computational Laboratory | de Leo V.,Complex Systems Computational Laboratory | Barthelemy M.,CEA Saclay Nuclear Research Center | And 3 more authors.
PLoS ONE | Year: 2012

Community detection is an important tool for exploring and classifying the properties of large complex networks and should be of great help for spatial networks. Indeed, in addition to their location, nodes in spatial networks can have attributes such as the language for individuals, or any other socio-economical feature that we would like to identify in communities. We discuss in this paper a crucial aspect which was not considered in previous studies which is the possible existence of correlations between space and attributes. Introducing a simple toy model in which both space and node attributes are considered, we discuss the effect of space-attribute correlations on the results of various community detection methods proposed for spatial networks in this paper and in previous studies. When space is irrelevant, our model is equivalent to the stochastic block model which has been shown to display a detectability-non detectability transition. In the regime where space dominates the link formation process, most methods can fail to recover the communities, an effect which is particularly marked when space-attributes correlations are strong. In this latter case, community detection methods which remove the spatial component of the network can miss a large part of the community structure and can lead to incorrect results. © 2012 Cerina et al.


PubMed | Complex Systems Computational Laboratory
Type: Journal Article | Journal: Physical review. E, Statistical, nonlinear, and soft matter physics | Year: 2013

This work analyzes methods for the identification and the stability under perturbation of a territorial community structure with specific reference to transportation networks. We considered networks of commuters for a city and an insular region. In both cases, we have studied the distribution of commuters trips (i.e., home-to-work trips and vice versa). The identification and stability of the communities cores are linked to the land-use distribution within the zone system, and therefore their proper definition may be useful to transport planners.

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